The long-range goals of this project are to understand the mechanical basis for activation of afferent neurons innervating joint capsules, and to develop a means for using joint capsule afferent neurons as a tool for studying joint capsule biomechanics. One specific aim is to relate responses of single mechanoreceptor afferents in cat knee capsule to precisely measured mechanical states at the location of the receptor in the capsule. Neurons will be studied in two capsule locations: a) the response of afferents located in the upper, cable-like edge of the capsule will be related to cable tension and b) the response of receptors in the capsule sheet will be related to measurements of stress, strain and strain energy density at the receptor location. The specific aim of both studies is to understand what mechanical variables are encoded by the discharge of capsule afferents. A second specific aim is to use recordings of joint afferents to make deductions about the biochemical state of the knee joint capsule. Tension in the capsule cable, and strain energy density in known locations in the capsule sheet will be judged using the responses of capsule afferents recorded during complex rotations or loadings of the joint.. A third specific aim is to characterize the mechanical sensitivity of fine myelinated A-d, and unmyelinated "c" fibers in the posterior articular nerve in the cat. A fourth specific aim is to investigate the mechanical relationship between mechanoreceptors and the collagen structure of the capsule. Collagen structure and receptor structure will be visualized in isolated, innervated rat knee capsule, using optical methods. Collagen deformations and receptor deformations will be related to receptor activation.